This invention relates generally to tools and instruments and, more particularly, to instruments known as a spirit or carpenter's level.
The carpenter's level, long used by carpenter's, bricklayers and others in the building trades for finding a horizontal level or plane, consists of an elongate body, typically formed of wood or extruded metal such as aluminum, which supports three spirit levels. Each level serves to find a horizontal line or plane by means of a bubble in a non-freezing liquid, usually mineral spirits, that shows adjustment of the horizontal by movement of the bubble to the center of a glass tube that is slightly bowed up from the horizontal longitudinally. The vial of a first level is mounted with its long axis parallel to the longitudinal axis of the body, and two additional levels are mounted near the ends of the body with their long axes oriented perpendicularly to the first. The accuracy with which a horizontal or vertical plane can be determined is critically dependent on the accuracy at which the bubble is centered between transverse lines etched or painted on the glass vial which, of course, is dependent on the visibility of such lines and the outline of the bubble itself. While the position of the bubble can readily be seen under normal lighting conditions, it becomes difficult to see on a heavily clouded day, or at dusk, or in poorly lighted spaces. That is to say, the conventional carpenter's level can be effectively used only in relatively well-lighted environments and, accordingly can put constraints on the times and places craftsmen such as carpenters and bricklayers are able to work efficiently. Since only the bubble and the transverse lines on the vial need to be observed to locate the center position of the bubble, the use of the level could be greatly expanded, including to night time use, by illuminating the bubble vial.
It is a primary object of the present invention to provide a carpenter's level having selectively illuminated spirit levels.
Another object of the invention is to provide a carpenter's level having self-contained means for automatically illuminating either the horizontal spirit level or the plumbing spirit levels in dependence on the orientation of the level.
Still another object of the invention is to provide a carpenter's level of the character described having a self-contained long-life energy source for illuminating the spirit levels.
SUMMARY OF THE INVENTION
Briefly, each of the bubble vials of a carpenter's level is illuminated by a suitable light source, such as a light-emitting diode (LED) disposed adjacent one end thereof, the light source being energized from a rechargeable battery supported within the body of the level. The battery charge is maintained by one or more solar cells mounted on an exterior surface of the body of the level so as to deliver charging current to the battery during daylight hours. The circuit for energizing the light sources includes a manually-actuable on-off switch, preferably positioned on the body to be switched OFF when the level is hung on a hook, for example, and a pair of orientation-dependent switches, such as a simple mercury switch, supported at different orientations within the body such that one of them closes when the level is positioned horizontally to apply voltage across the light for the horizontal bubble vial, and the other connects the battery across the lights for the bubble vials of the plumbing levels when the body is vertically oriented. That is, the circuit is operative to automatically illuminate only the bubble vial or vials that need to be illuminated to observe the position of the bubble for the orientation selected by the user.
Other objects, features and advantages of the invention, and a better understanding of its construction and operation, will be had from the following detailed description, taken in conjunction with the accompanying drawings.